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Old 04-26-2017, 01:30 PM   #1
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What is acceptable 12v voltage drop/ line loss?

Hi!
I'm new to this forum and 3 days into RV ownership lol! I'm very inexperienced with RV's but and soaking up as much info as I can.
I recently purchased a 2004 27SD Jayco grey hawk.
While it was sitting in my driveway I started hearing a beep every 20 seconds or so. I located the source of the beep and it was the LP/carbon monoxide detector indicating fault/low voltage.
I pulled it out and metered the wires feeding the detector and am reading 11.5V. If I meter the terminals of my house battery it reads 12.6V. I also metered one of the 12V ceiling lights and only has 11V.
I'm concerned I'm having higher than usual voltage drop between my battery and the 12v wiring in the motor home. It does have a momentary switch that activates a solenoid for house battery disconnect. Could this device cause my issues? Is a one volt drop normal in these things? How low can a Safe T Alert sensor operate voltage wise before it beeps low voltage?

Thanks in advance!!! I'm super excited about getting this thing ready for my first overnight trip
Brian
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Old 04-26-2017, 01:33 PM   #2
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If I go below 12 volts I start getting concerned. That's when the generator kicks in if I'm off grid.

If you have any 12 volt cigarette style sockets in your camper, you can get a 10 dollar plug at amazon for it that will show you what your inside wiring is showing as far as charge goes. It has some USB charging ports on it too.

I've had my smoke / monoxide detector alarm like that before when my battery was well above 12 volts. I don't trust it / am not convinced it's always telling the truth.
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Old 04-26-2017, 01:40 PM   #3
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Are you sure you were checking the house battery vs the starting battery. I don't think you should get that kind of voltage drop anywhere in the system.

Something funny going on....

Generally you don't want to go below 12v (50% discharged) for any 12v lead acid battery. Fully charged should be around 12.6 to 12.7 volts

Cheers
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Old 04-26-2017, 01:55 PM   #4
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Are you sure you were checking the house battery vs the starting battery. I don't think you should get that kind of voltage drop anywhere in the system.

Something funny going on....

Generally you don't want to go below 12v (50% discharged) for any 12v lead acid battery. Fully charged should be around 12.6 to 12.7 volts

Cheers
My thought exactly, perhaps not checking the coach battery voltage.
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Old 04-26-2017, 01:57 PM   #5
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I have a fluke multimeter and I'm sure it was the house battery as it was on a slider tray located at the rear driver side of the RV. When I meter the posts I get 12.6v. When I metered the wires that fed the detector I read 11.5v. I also pulled a light bulb out of a ceiling fixture and read 11v. I googled voltage drop and for 16 gauge wire at 25' it should only drop less than 1/4 v. I suspect something is causing a loss of voltage through a bad ground or connection. Just not sure where to find the connections lol
Thanks for the replies!!
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Old 04-26-2017, 02:05 PM   #6
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Perhaps you might also try checking the voltage at the electrical panel where all your house (12-volt) fuses are located. If it is nearly the same as the house battery's you may find the issue is limited to a single circuit. If it is low at the panel affecting all circuits you may have an issue between the battery and the panel.
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Old 04-26-2017, 02:13 PM   #7
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Congratulations on your new MH.

Your voltage at the battery is right in the proper range for a fully charged battery. If you were connected to shore power, I would expect your voltage to be much greater as the inverter would be charging the battery.

Have you plugged in the MH to shore power and taken voltage readings? Also if the MH is just sitting there are parasite drains that will drain your battery within a few weeks, so it is best to keep it plugged in or use a battery disconnect.

My first thought is bad grounds. I would remove the battery, clean the posts, then find the other end of the ground strap, check it, clean it, including the frame mount. I always add a star washer to help bit into the frame.

On a TT everything is grounded to the frame, with some items like lights daisy chained, I would assume your MH is the same way. So I would crawl underneath and start checking grounds. I found a product that I really like, and use on old cars. It is called "Rail Zip" it was developed for the model railroad hobby. An old car guy that like cars that used Lucas connects, which are notoriously horrible lead me the product. Add drop or two to the connections and within a day they usually work as good as new, and it add a layer of protection from future corrosion.

Congratulations and good luck!
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Old 04-26-2017, 02:37 PM   #8
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Quote:
Originally Posted by Brian556 View Post
I recently purchased a 2004 27SD Jayco grey hawk.
While it was sitting in my driveway I started hearing a beep every 20 seconds or so. I located the source of the beep and it was the LP/carbon monoxide detector indicating fault/low voltage.
Hope you get the info you need on your voltage issue.

On a side note, be aware CO detectors have sensors that have only a 5-7 year lifespan and then the detector needs to be replaced. Check the mfg. date on yours to be sure it was made in 2011 or later.
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Old 04-26-2017, 02:42 PM   #9
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Congratulations on your new MH.

Your voltage at the battery is right in the proper range for a fully charged battery. If you were connected to shore power, I would expect your voltage to be much greater as the inverter would be charging the battery.

Have you plugged in the MH to shore power and taken voltage readings? Also if the MH is just sitting there are parasite drains that will drain your battery within a few weeks, so it is best to keep it plugged in or use a battery disconnect.

My first thought is bad grounds. I would remove the battery, clean the posts, then find the other end of the ground strap, check it, clean it, including the frame mount. I always add a star washer to help bit into the frame.

On a TT everything is grounded to the frame, with some items like lights daisy chained, I would assume your MH is the same way. So I would crawl underneath and start checking grounds. I found a product that I really like, and use on old cars. It is called "Rail Zip" it was developed for the model railroad hobby. An old car guy that like cars that used Lucas connects, which are notoriously horrible lead me the product. Add drop or two to the connections and within a day they usually work as good as new, and it add a layer of protection from future corrosion.

Congratulations and good luck!
Thank you so much for the information! The sensor does not beep when on shore power, generator, or while I'm driving. I will check all the grounds and hopefully I can find the disconnect solenoid. I know I have to hit the switch a couple time to get it to change state and I'm curious if it's causing a resistance issue.
Thanks again!!!
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Old 04-26-2017, 02:44 PM   #10
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Hope you get the info you need on your voltage issue.

On a side note, be aware CO detectors have sensors that have only a 5-7 year lifespan and then the detector needs to be replaced. Check the mfg. date on yours to be sure it was made in 2011 or later.
There is a date stamp on the back of my sensor for 2015. It doesn't indicate if that was the date of manufacture or expiration date lol. Any idea which it is??
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Old 04-26-2017, 02:55 PM   #11
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There is a date stamp on the back of my sensor for 2015. It doesn't indicate if that was the date of manufacture or expiration date lol. Any idea which it is??
If it doesn't say "replace by" it's almost certainly the date of mfg. If your RV is a 2004 model and the previous owner(s) were safety-conscious and replaced the detector after every 5-6 years, then a 2015 date would make sense.

And yes, check the ground for sure. Many years ago I had a problem similar to yours and, after trying everything else discovered a corroded chassis ground wire connection.
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Old 04-26-2017, 02:59 PM   #12
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Yank another 12V fixture - like a light - and check the voltage???

I'm about as far from an EE as you can get, but I've read RV electrical is "different". They're floating ground, if I'm saying that correctly.

Dunno what that means, but thought I'd pass it along.
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Old 04-26-2017, 05:38 PM   #13
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Do you get roughly the same voltages when you go positive terminal to frame / positive lead at detector to the frame?
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Old 04-26-2017, 06:55 PM   #14
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Do you get roughly the same voltages when you go positive terminal to frame / positive lead at detector to the frame?
I didn't check that but will. Just have to get creative on getting my neg lead to a good frame ground point while reaching the hot wire at the detector. Might need to get some alligator clamps or something
Thanks for the advice!
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Old 04-26-2017, 08:03 PM   #15
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I think another person commented, but just trying to rule out a chassis grounding issue. That would definitely explain why your battery is good but other things aren't.
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Old 04-26-2017, 08:44 PM   #16
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Brian,
To answer your original question - "what's an acceptable voltage" here's a typical 12v battery charge level table:
http://www.marxrv.com/12volt/voltchart1.gif
I have this taped up next to my voltmeter.
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Old 04-26-2017, 09:09 PM   #17
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Brian,
To answer your original question - "what's an acceptable voltage" here's a typical 12v battery charge level table:
http://www.marxrv.com/12volt/voltchart1.gif
I have this taped up next to my voltmeter.
I have a laminated copy of this same chart in my tool box
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Old 04-26-2017, 09:53 PM   #18
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My thoughts...your battery is dead, despite the voltage readings.

I suspect if you were to pull a known good battery (like from a car you use all the time) and put it temporarily in place of your house battery, your voltage at your outlets and lights would be in the proper range. Not sure why this is, but I ran into a similar issue with a neighbor's lawn mower battery the other day. His battery was showing right at 12.6 volts on a known good multi-meter (one of several I own), but it wouldn't turn the motor over.

Recommend you change out the battery with another you already have (starting battery?) and give it a try. If I'm wrong, the only thing you've lost is a little bit of time and effort.
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